In this type of PoC systems, one-to-many telephone conversation can be made with use of packet networks (see published Japanese patent translation No. 2003-526275, for example). However, two or more persons cannot speak simultaneously. One who wants to speak has to wait for a currently speaking person to finish his/her speaking, then gets the right of speaking, and begins to speak.
The way to use portable terminals in PoC communication is similar to the way to use transceivers. When a speaker pushes down an exclusive key and holds it down, he/she obtains the right of speaking to transmit voice data of his/her speaking to other portable terminals. No one can speak with the other portable terminals, which can only receive the voice data. When the person who has the right of speaking releases the exclusive key, the right of speaking is released. A portable terminal in which the exclusive key is first pushed down after the right of speaking has been released gets the right of speaking, which allows speaking through that portable terminal.
The right of speaking in PoC is managed by a PoC server. The PoC server performs registration of members, recognition of participation availability information such as “absence” or “presence” of members, assignment of the right of speaking, and the like. The recognition of participation availability may be called as presence function. The assignment of the right of speaking may be called as floor control.
In PoC portable terminals used in the aforementioned PoC system, there is a method in which users make a group telephone conversation while they see screen information relating to the group telephone conversation on screens of their PoC portable terminals.